Homework answers / question archive / Homework - I (CHEM 2325-03) Fall 2016 [General Review, Aromaticity & Electrophilic Aromatic Substitution]                         Must be turned in through Blackboard as “Course Message” attachment (single PDF file)  DEADLINE of Submission is 10/12/2016 by 11:59 PM     Short answer/Multiple type questions 1

Homework - I (CHEM 2325-03) Fall 2016 [General Review, Aromaticity & Electrophilic Aromatic Substitution]                         Must be turned in through Blackboard as “Course Message” attachment (single PDF file)  DEADLINE of Submission is 10/12/2016 by 11:59 PM     Short answer/Multiple type questions 1

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Homework - I (CHEM 2325-03) Fall 2016

[General Review, Aromaticity & Electrophilic Aromatic Substitution]

                        Must be turned in through Blackboard as “Course Message” attachment (single PDF file) 

DEADLINE of Submission is 10/12/2016 by 11:59 PM

 

 

Short answer/Multiple type questions

1. In case of covalent non-polar bond the difference in electronegativity between two bonded atoms is ?

2. In case of covalent polar bond the difference in electronegativity between two bonded atoms is ?

3. If the electronegativity difference between two bonded atoms is higher than -----  the bond is called ionic bond.
4. Higher the electronegativity difference between two bonded atoms, more -----  is the covalent bond.
5. Carbon is ----  hybridized in methane whereas ---  hybridized in ethylene.

6. Carbon is ----  hybridized in ethane whereas ---  hybridized in acetylene.
7. How many σ-bond and π-bond are present in ethylene (C₂H₄) molecule?
8. How many σ-bond and π-bond are present in acetylene (C₂H₂) molecule?
9. In benzene, the carbons are ----  hybridized.

10. As the number of nearly equivalent resonance contributors ------ , the resonance energy ------.
11. The carbonyl carbon in acetic acid is ----  hybridized whereas the carbon in methanol is -----.
12. The carbonyl carbon in acetic acid contains ----   s-character whereas the carbon in methanol contains ---  s-character.
13. EDG (electron donating group) stabilizes the  --------  making the reaction ------  whereas EWG (electron withdrawing groups) destabilizes the carbocation making the reaction
14. -----  is an activating group in EAS (electrophilic aromatic substitution) whereas ------  is a deactivating group.
15. The halogens ------------  the benzene ring in electrophilic -----------  substitution.
16. All ---------  derectors deactivate the benzene ring.
17. Write the structure of TNT.
18. The Carbon-Carbon bond distance in ethylene is ------- Å whereas Carbon-Carbon bond distance in benzene is----------  Å. 
19. What is the major product in the following reaction?

                                          

Free response questions

 

1. 9. 1. Why do atoms bond?
      2. What is electronegativity?
      3. What do you mean by dipole moment? Explain, considering water molecule as an example
      4. Why chloroform (CHCl₃) is polar whereas carbon tetrachloride (CCl₄) is non-polar?
      5. NH₃ is a polar molecule but BF₃ is non-polar—justify
      6. What do you mean by (i) σ-bond and (ii) π-bond? Explain.
      7. Explain the terms “resonance contributor” and “resonance hybrid” considering benzene as an example.
      8. What makes resonance structure have decreased stability?
   10. The double bond in cyclohexene can be oxidized by potassium permanganate (KMNO₄), whereas the double bonds in benzene do not undergo this oxidation reaction — Justify.
   11. Draw the orbital diagram of benzene.
   12. Benzene is aromatic whereas 1,3,5-hexatriene is nonaromatic — Explain.
   13. Cyclooctatetraene is a cyclic molecule with conjugated π-system having 8 π electrons but it is non-aromatic — Why?
   14. Write the two aspects of the electrophilic aromatic substitution reaction that are affected by a substituent? OR how the rate of the reaction and orientation are affected in EAS?
   15. Define the terms:
   16. Write the four requirements of a molecule to be aromatic.

 

1. 17. Explain Hückel’s Rule of aromaticity with examples.
   18. Cyclobutadiene is not available to purchase directly from the market — Why?
   19. Clarify the terms: (a) Bonding MO (b) Antibonding MO (c) HOMO (d) LUMO 

 

1. 20. Pyrrole is a heteroaromatic five membered (I) organic base (pKa = 0.4) whereas pyridine is a heteroaromatic six membered (II) organic base (pKa = 5.25). Explain why pyridine is 13 times more basic than pyrrole.

 

1. 21. Halogens are electron withdrawing but are ortho/para director in electrophilic aromatic substitution-Explain.
   22. What is electrophilic acylium cation? How does it form and affect Friedel-Crafts acylation reaction?
   23. Go over the examples of the four rules related to additivity of substituent effects in the case of EAS.

 

1. 24. Ethyl benzene is treated with (i) Br₂ and FeBr₃ and (ii) Br₂ and light or heat separately. Do you think the products will be same? Justify your answer.
   25. Go through the oxidation and reduction products of substituted benzenes. Which reagents are used for (i) Clemmensen reduction and (ii) Wolff-Kishner reduction?
   26. Two hydrogen atoms can combine to form H₂ but two He atoms cannot form He₂ — Justify from MO viewpoint.
   27. What is ipso substitution? Give an example [structures need to be drawn].
   28. Why aromatic compounds are more stable than their aliphatic counterpart? Draw the MO diagram of benzene.
   29. Explain the terms “Aromatic”, “Non-aromatic” and “Antiaromatic” considering the examples of Cyclopentadienyl anion, Cyclopentadienyl radical and Cyclopentadienyl cation respectively. 
   30. Cycloheptatrienylium cation is more stable than Cycloheptatriene — Why?
   31. Cyclopropenyl cation is a planar molecule. Is it “Aromatic”, “Non-aromatic” or “Antiaromatic”?
   32. Imidazole with 8 π electrons is aromatic — Why?
   33. Furan with 8 π electrons is aromatic — Why?
   34. Thiophene with 8 π electrons is aromatic — Why? Pyrene with 16 π electrons is aromatic — justify.
   35. The compound [10] Annulene is not aromatic — Justify.
   36. What do you mean by “Pericondensed” and “Catacondensed” polycyclic aromatic hydrocarbons (PAHs) ? Give two examples in each case (structures are required).
   37. EAS can be considered as Lewis acid-Lewis base reaction — Justify.
   38. How the electrophilicity of bromine (a weak electrophile) can be increased by using FeBr₃?
   39. Write the name of the electrophiles in nitration and sulfurnation reactions?

 

1. 40. Write the difference between ‘reagent’ and ‘catalyst’ of a reaction.

 

 

 

 

1. 41. 

       What is the ‘missing reagent’ in the following reaction?
   42. Write the mechanism of the following reaction:
   43. Write the mechanism of the following reaction:
   44. Write the mechanism of the following transformation:
   45. Write the mechanism of the following transformation:
   46. Write the mechanism of the following transformation:
   47. Write the mechanism of the following transformation:
   48. Write the mechanism of the following transformation:
   49. Why n-Propylbenzene cannot be synthesized by Friedel-Crafts alkylation reaction
   50. Write the name and structure of the electrophile in ?

 

 

 

 

Representative multiple choice questions

1. As energy of MO increases, the number of nodes
   1. decreases
   2. remains same
   3. increases
   4. either (a) or (b)
   5. none of the above

 

2. The name of the following compound is:

  

2. 1. Tetrabenzene
   2. Chrysene
   3. Coronene
   4. Anthracene
   5. Pyrene
3. To achieve noble gas configuration, hydrogen requires………………..whereas chlorine requires…………………in outermost shell. a. Octet, duet
   2. Singlet, duet
   3. Duet, octet
   4. Octet, singlet
   5. None of the above
4. The ……………. the number of relatively stable resonance contributors, the …………… the resonance energy.

a. Higher, lower

4. 2. Lower, higher
   3. Higher, higher
   4. Lower, lower
   5. None of the above
5. The name of the following compound is:

 

1. 1. Benzene
   2. Toluene
   3. Formaldehyde
   4. Benzaldehyde 
   5. Crotonaldehyde

 

 

6. Phenanthrene is ----------------, ---------------- compound.

 

6. 1. Bicyclic, aromatic
   2. Substituted, antiaromatic
   3. Tricyclic, aromatic
   4. Alcoholic, nonaromatic
   5. Acidic, antiaromatic
7. The number of π (pi) electrons in anthracene is:

 

 

1. 1. 6;     b. 8;        c. 10;      d. 12;      e. 14

 

 

 

8. Thiophene is a ---------------------------compound.

 

 

8. 1. Five membered carbocyclic
   2. Six membered heterocyclic
   3. Seven membered cyclic
   4. Five membered heteroaromatic 
   5. Aliphatic
9. The name of the following compound is:

 

9. 1. Imidazole
   2. Indole
   3. Pyridine
   4. Thiophene
   5. Pyrrole
10. A four membered, cyclic, planar, completely conjugated compound with sp² hybridized carbons and 4? (pi) electrons will be:   a. Heteroaromatic               b. Aromatic          c. Nonaromatic             d. Antiaromatic           e. None of the above

 

11. The following planar cation will be:

 

11. 1. Aromatic
    2. Heteroaromatic
    3. Antiaromatic
    4. Both (a) & (b)
    5. Nonaromatic
12. As energy of MO increases, the number of nodes
    1. decreases
    2. remains same
    3. increases
    4. Either (a) or (b)
    5. None of the above
13. The name of the following compound is:

 

13. 1. Pyridine
    2. Pyrrole
    3. Pyrimidine
    4. Indole
    5. Imidazole
14. Atorvastatin (Lipitor), the top selling marketed drug, is a derivative of
    1. Pyrrole
    2. Indole
    3. Thiophene
    4. Imidazole
    5. None of the above
15. The compound furan is ……………….

 

1. 1. aliphatic nitrogen heterocycle
   2. aromatic nitrogen heterocycle
   3. carbocyclic sulfur heterocycle 
   4. aromatic oxygen heterocycle
   5. aliphatic oxygen heterocycle

 

16. The name of the following compound is……………..

 .

1. 1. Indole
   2. Pyrimidine
   3. Naphthalene
   4. Purine
   5. None of the above

 

17. Carbocation is a typical……………….
    1. Aromatic compound
    2. Heteroaromatic compound
    3. Monocyclic compound
    4. catalyst
    5. electrophile

 

18. In Friedel-Crafts acylation reaction of benzene, the electrophile is 
    1. Benzene
    2. Acylium ion
    3. Alkyl radical
    4. Lewis base
    5. None of the above

 

19. Lewis acid is
    1. Electron pair acceptor
    2. Electron pair donor
    3. Aromatic compound
    4. Proton donor
    5. None of the above

 

20. In Friedel-Crafts reaction new bond formation takes place between:
    1. Carbon and a nitrogen atom
    2. Carbon and a bromine atom
    3. Carbon and a sulfur atom
    4. Two carbon atoms
    5. No new bond is formed

 

21. The stability of the carbocations is as follow:
    1. 1? carbocation > 2? carbocation > 3? carbocation
    2. 2? carbocation > 3? carbocation > 1? carbocation
    3. 2? carbocation > 1? carbocation > 3? carbocation
    4. 3? carbocation > 2? carbocation > 1? carbocation
    5. None of the above

 

22. In the reaction “sulfonation of benzene” the name of the product is
    1. Benzene sulfanilic acid
    2. Benzene sulfonamide
    3. Sulfanilic acid
    4. Benzenesulfonic acid
    5. Nitrobenzene

 

23. The main product in the Friedel-Crafts acylation reaction is:
    1. Alkyl halide
    2. Carbocation
    3. Alcohol
    4. Bromobenzene
    5. Ketone